CALIBRATING HORIZONTAL-BRANCH STARS WITH HIPPARCOS

Parallaxes from the Hipparcos satellite allow for the first time to ca librate parameters of horizontal-branch (HE) like stars based on geome tric distances. We present absolute magnitudes and luminosities for 8 such stars. Using T-eff and log g values available from the literature , we also can calculate the mass of the HE stars. We find an average v alue of M(HB) = 0.38 +/- 0.07 M. for stars with 7500 < T-eff < 9000 K, well below the value from stellar evolution theory, which predicts ma sses near 0.6 M.. Recent investigations of HE stars in globular cluste rs indicated similarly low mass values. The likely cause for the discr epancy of the mass values lies in the low gravities derived from Balme r line profiles.